All centralized exchanges would shut down if that happened. Then truly decentralized exchanges would thrive. Let's see them skin the sheep.
You must be new here, but your "legendary" status says otherwise. What did Gox, BTC-e and Stamp all do 2 years ago before we broke above $100? Were they losing their asses or did they open up because they knew it was a lucrative business even below $100?
I'd actually wager a guess that they make more money at lower prices because volumes are higher and more people are able to buy more with the same balance. Their actual USD fees wouldn't change much if at all but their BTC fees would double. Win win.
"You can sheer a sheep many times, but skin it only once." In bitcoin's case meaning unregulated central exchanges will be finally exposed as bad for bitcoin because they favor fiat profit taking. Even Wall Street doesn't allow such volatility. Decentralized exchanges will slow down trading and allow natural price discovery without panic trading. Also such low prices are boring and nobody will care anymore. Bitcoin will go back to hobby status until the next development wave creates more disruptive technology that eliminates exchanges entirely.